jth877

Doubt it's the valve train unless it was really low on oil for extended period of time. With Mobile1 it's whole life the engine SHOULD be very clean. Switch to 10W30. I'm not sure of the zddp levels between mobil1 5w30 vs. 10w30. My engine quiets down quite a bit with oils that have over 1000ppm of zinc.

The other areas to check: Just about every friggin pulley. Water pump and AC are two that tick a lot when worn out.

jeepkid03

I was suggested by a few on an oil forum to try 10w40 Valvoline MaxLife with a half quart of 5w20 synthetic mixed in. I laughed but tried it anyway. I was pleasantly surprised that my engine is much quieter. I tried everything in the book from Marvel Mystery Oil to thicker oil to zddp additives, synthetic, conventional, Lubri Moly MoS2, you name it. The 1/2 quart 5w20 synthetic has worked the best.

french

My problem with the tapping type of noise I had, was the little vacum pump on the fire wall. Sounded just like engine tapping. Used the tube to ear method.
Replaced and quiet. 2000 xj 5 speed 4.0. Just a thought.

99FreshenedCherokee

mine DID run with very little oil for an extended period of time.....then when i changed my oil and saw that i was missing at least two quarts the dreaded tapping noise came up..

00maroonXJ

So it sounds like it could be a variety of things... RE:the water pump.... if it is about seized up, would there not be fluid coming out the pee hole, or is that JUST to tell if the bearing is bad? Also, my water pump gasket was leaking, so I used some aluminol and that definitely stopped the leak...Is there any other way to diagnose if you have a bad water pump besides actually pulling it? Sorry for the long-windedness of this....

myk'98cherokee

i have a 98 cherokee and it taps at a stop but when i accelerate it go's away, does anyone have any ideas

Sincebeen

It's funny but I just flushed/changed my coolant yesterday and that's when I started to hear the diesel sound... Like immediately after.

I did change my oil a couple days ago but the coolant is what really changed the sound a lot.

Looks like a new water pump is in order...

Sincebeen

Got the new water pump on yesterday, all new hoses too, and the noise is still there. Bummer! I think it might be the pulley next to the water pump.

Back to the drawing board

Zack92MJ

Mine taps when a first start it up and its waring up

99FreshenedCherokee

Ok so I just foud out that the tap i had was coming from the distributor cap and rotors, I repolaced'm both and it went away.

incrediblehawk

i have 00 and it was diagnosed as a sticky lifter/screwed rocker arm (goin by memory)

well they were right, then after pressure test on the head, they found a hair line crack. SO my 119k engine has a head with less than 1k miles... I am hoping this beast lasts forever now.

Yes, thats how much I love my Jeep.

He went on to tell me common problems with the 2000. AC Evaporator, Electric window opener, ac/heat switch and relay, leaky trans pan, leaky head cover gask... otherwise a champ of a vehicle...

went outside, the guy had a 2000 and "wouldnt trade it for the world"

codyd

So I have a knock thats coming from mid to lower part of engine. It sounds like a diesel engine after reading several post I would assume its a rod knock but it doesnt have the loud clunk that a rod knock would have. I just bought it about a month ago and after adding the exhaust and changing the oil I noticed the noise. If theres something I can do to quieten it down let me know any help would be appreciated.

Sincebeen

Well there's a minimum of two different noises in this thread. The first one in question, for the new Jeep owner, is the rumbling that sounds like its coming from under the engine near the oil pan. This noise is present all the time and is, as far as I can tell, normal. And proving to yourself that it's normal is easy; just find someone else with a Jeep and listen to theirs. They ALL do it. Fresh new oil doesn't seem to do the noise any favors either. Just about every engine i've owned (including the 5.4L Ford Triton, 5.7L Hemi, and this 4.0L) has ran louder after putting new synthetic oil in. I was thinking about running a thicker oil next change but not sure yet.

The second noise is the loud diesel tap that goes away when the engine gets to normal temperature. I think this is the one we're trying to figure out. Somewhere in this thread there's some advice about using a piece of hose like a stethoscope. I keep a ~3 ft length of garden hose and was able to pinpoint the noise to the water pump.... area. It turns out that the water pump wasn't the problem (in my case) but I know the noise is close by. The reason the hose is so helpful is because of the echo under the hood. The noise sounds like it's coming from the oil pan but when you use the hose you may find the inside of the crank case sounds normal.

.

Scott_Sport99

I have that noise also. I think tomorrow I will take off the serp belt and see if it goes away to narrow it down.
I bought the truck a month ago. put 500 miles on it with no sounds. started doing tlc and changing old parts almost to where I want it and now the "knock" sound.
So I am in the boat with you all lol.
I'll let ya know what I find..I will find it, that is just my OCD

On a side note My friend just picked up a GK Limited with the I6 and he has the sound also.

PS On a 99 how the heck do you get the bolt out to remove the inspection cover for the flex plate? I tried today but only checked the torque converter bolts cause I could not get that freaking plate off..I think I may dremel a little piece off to get it down to check the flex bolts..rather stupid idea Jeep had on that one.

I just found this vid and this is the sound I have so I guess I really need to get the cover off to see if I have to pull the tranny.